Device and method for acoustic diagnosis and measurement by pulse electromagnetic force

ABSTRACT

The invention provides an acoustic diagnosis/measurement apparatus/method using a pulse of electromagnetic force, capable of non-destructively and precisely diagnosing or measuring corrosion, adhesion, the. cover depth, and/or the diameter of a reinforcing iron rod in a structure made of reinforced concrete. A coil  12  is attached to a surface of a structure  11  including a conductor  11   a  and a non-conductive material  11   b  covering the conductor  11   a . A current pulse is applied to the coil  12  thereby generating a magnetic field pulse. The magnetic field pulse causes an eddy current to be induced in the conductor  11   a . The conductor  11   a  is oscillated by interaction between the eddy current and the magnetic field pulse. As a result, an acoustic signal is generated by the conductor  11   a  and the acoustic signal is converted into an eclectic signal by an acoustic transducer  14  disposed to the surface of the structure  11 . The resultant electric signal is measured by a measurement unit  15  to diagnose/measure the location of the conductor  11   a  or the state of the structure  11 .

TECHNICAL FIELD

[0001] The present invention relates to an acousticdiagnosis/measurement apparatus using a pulse of electromagnetic forcefor diagnosing/measuring a structure including a conductor and anon-conductive material covering the conductor, and a method ofdiagnosing/measuring such a structure, in particular, in terms ofcorrosion or adhesion of a reinforcing iron rod in reinforced concrete,the location of the reinforcing iron rod, the diameter of thereinforcing iron rod, presence/absence of a fracture in the reinforcingiron rod, or the location of the fracture, or in terms of the locationof a water pipe buried in the ground, or in terms of whether a conductoris securely bound by a binding member.

BACKGROUND ART

[0002] In a structure made of reinforced concrete, such as a tunnel, abridge, a building, a retaining wall, a dam, or a civil construction, inorder to evaluate the strength or life or to determine constructionprocedure, it is needed to detect locations of reinforcing iron rods,diameters of reinforcing iron rods, the degree of corrosion ofreinforcing iron rods, and/or adhesion strength of reinforcing ironrods, for the purpose of, for example, evaluation of strength or life ofthe structure or determination of procedure of construction. Varioustechniques for the above purpose are known. They include radiography fortaking an X-ray image of a structure placed between an X-ray generatorand a film, ultrasonic diagnosis in which an ultrasonic wave isgenerated by an ultrasonic generator placed on the surface of concreteand diagnosis/measurement is performed on the basis of detection of areflected ultrasonic wave, a percussion method in whichdiagnosis/measurement is performed on the basis of an echo detectedafter tapping a surface of a structure with a hammer or the like, aninfrared imaging method in which a surface of a structure is illuminatedwith an infrared ray, and a microwave method in which a surface of astructure is illuminated with a microwave.

[0003] However, the conventional methods of detecting locations ofreinforcing iron rods or corrosion of reinforcing iron rods haveproblems as described below. For example, in radiography, it is neededto put a structure between the X-ray generator and the film, and thusthis method has various limitations such as those on the shape, thesize, and the location. This method cannot be substantially used fortunnels, dams, or the like. Another problem is that control is needed soas to prevent a human body from being significantly damaged by an X-rayand thus it is not easy to employ this method.

[0004] In the detection of the locations of reinforcing iron rods usingthe percussion method, a high skill is needed. Because detection isbased on the skill, it is difficult to achieve high reliability indetection. When diagnosis of corrosion is performed using this method,corrosion cannot be easily detected unless reinforcing iron rods are sosignificantly corroded that a void is created. In this method, detectionof corrosion is based on the skill and thus the reliability of detectionis low. For this reason, it is needed to partially expose a reinforcingiron rod and visually observe an exposed part to confirm.

[0005] In the ultrasonic diagnosis method, an ultrasonic wave is appliedto the surface of reinforced concrete, and the location of a reinforcingiron rod is determined from an ultrasonic wave reflected from thereinforcing iron rod. However, the concrete includes gravel and a largenumber of non-continuous parts created by bubbles or the like, whichcause the ultrasonic wave to be attenuated or scattered and thus make itdifficult to perform analysis.

[0006] In the infrared imaging method and also in the microwave method,because the infrared ray or the microwave is greatly attenuated byconcrete, measurement is possible only in a region near the surface of astructure.

[0007] As a for a method of diagnosing corrosion, it is known to detectan acoustic wave generated by elastic energy released when a structureis deformed or cracked and analyze the detected acoustic wave todetermine the degree of corrosion of the structure. This method is knownas an acoustic diagnosis method. More specifically, an acoustic emission(AE) sensor is attached to a structure and the output of the AE sensoris monitored over a long period of time to detect an acoustic emissionwhich occurs accidentally and suddenly due to stress corrosion cracking.However, it is needed to continuously perform measurement over a longperiod and it is also needed to apply an unnecessarily large load. Thus,this technique is not suitable for detection of corrosion of astructure.

[0008] As described above, no conventional method is known which allowshigh-reliability non-destructive detection of the degree of corrosion ofreinforcing iron rods in reinforced concrete, adhesion strength betweenconcrete and reinforcing iron rods, or the location or the diameter of areinforcing iron rod in concrete. The lack of effective methods causesan error to occur in prediction of strength or life, and thus can causean unpredictable disaster to occur.

[0009] In structures including a prestressed conductor and anon-conductive material covering the conductor, that is, structures madeof prestressed-concrete, such as bridges, electric poles, and railroadties, reinforcing iron rods prestressed so as to enhance theirelasticity are embedded in concrete. When such a structure is used for along period, there is a possibility that a reinforcing iron rodfractures. However, no conventional technique is known which allows sucha fracture to be detected in a non-destructive fashion. Therefore,periodical replacement at scheduled intervals is needed, or otherwise anunpredictable disaster can occur.

[0010] In a civil engineering work or a construction work in which it isrequired to drive stakes into ground, it is necessary to know thelocations of existing water pipes or gas pipes buried in the ground. Inthis case, water pipes and gas pipes are conductors embedded in anon-conductive material. Conventionally, a metal detector or sonar isused to determine the buried location. However, such an apparatus iscomplicated and special technical knowledge is needed to handle it.There is no technique which can be easily used to detect a preciselocation under ground. Thus, in many cases, a troublesome job, such asdigging up the ground, is needed to make confirmation.

[0011] In the case of a structure including a plurality of conductorsbound with each other via a binding member, such as a bridge constructedas a road by joining iron plates using bolts and nuts, for the purposeof safety, it is necessary to periodically examine whether bolts andnuts are maintained in a securely fastened state. However, in structureshaving a large size such as bridges, large bolts and nuts are used andthey are fastened by very large torque. Therefore, it is impossible tomanually diagnose using a torque wrench or the like, and diagnosis isperformed using a dedicated machine having a large size. Another problemin such diagnosis is that it is necessary to close the bridge during thediagnosis.

[0012] In view of the above, a first object of the present invention isto provide an apparatus for diagnosing or measuring, non-destructivelyand precisely, a structure including a conductor and a non-conductivematerial covering the conductor in terms of the degree of corrosion, theadhesive strength, the cover depth, and the diameter of the conductor. Aspecific example is an apparatus for non-destructively diagnosing ormeasuring the degree of corrosion of reinforcing iron rods in reinforcedconcrete, the strength of adhesion between reinforcing iron rods andconcrete, and/or the cover depth or the diameter of reinforcing ironrods in concrete.

[0013] A second object of the present invention is to provide anapparatus for non-destructively and precisely measuring the location ofa concoctor in a structure including the conductor and a non-conductivematerial covering the conductor. A specific example is an apparatus fornon-destructively and precisely measuring the location of reinforcingiron rods in reinforced concrete.

[0014] A third object of the present invention is to provide anapparatus for diagnosing or measuring, in detail, the degree ofcorrosion, the adhesion strength, and/or the location of a conductor ina structure including the conductor and a non-conductive materialcovering the conductor, on the basis of a distribution of smallvibrations over the entire surface and a propagation mode of vibrations.A specific example is an apparatus for non-destructively diagnosing ormeasuring the degree of corrosion of reinforcing iron rods in reinforcedconcrete, the strength of adhesion between reinforcing iron rods andconcrete, and/or the location of reinforcing iron rods in concrete.

[0015] A fourth object of the present invention is to provide a methodof non-destructively and precisely diagnosing or measuring the degree ofcorrosion and/or the adhesion strength of a conductor in a structureincluding the conductor and a non-conductive material covering theconductor. A specific example is a method of non-destructivelydiagnosing or measuring the degree of corrosion of reinforcing iron rodsin reinforced concrete and/or the strength of adhesion betweenreinforcing iron rods and concrete.

[0016] A firth object of the present invention is to provide a method ofnon-destructively and precisely measuring the location of a conductor ina structure including the conductor and a non-conductive materialcovering the conductor. A specific example is a method ofnon-destructively measuring the location of reinforcing iron rods inreinforced concrete.

[0017] A sixth object of the present invention is to provide a method ofnon-destructively and precisely measuring the location of a conductor ina structure including the conductor and a non-conductive materialcovering the conductor. A specific example is a method ofnon-destructively diagnosing or measuring, in detail, the degree ofcorrosion of reinforcing iron rods in reinforced concrete, the strengthof adhesion between reinforcing iron rods and concrete, and/or thelocation of reinforcing iron rods in concrete, on the basis of adistribution of small vibrations over the entire surface and apropagation mode of vibrations.

[0018] A seventh object of the present invention is to provide a methodof measuring the diameter or the cover depth of a conductor in astructure including the conductor and a non-conductive material coveringthe conductor. A specific example is a method of measuring the diameteror the cover depth of reinforcing iron rods in reinforced concrete.

[0019] An eighth object of the present invention is to provide a methodof diagnosing or measuring whether conductors bound with each other viaa binding member are in a state in which the conductors are securelybound by the binding member. A specific example is a method ofdiagnosing or measuring whether iron plates bound with each other via abolt and a nut are in a state in which the iron plates are securelybound by the bolt and the nut.

[0020] A ninth object of the present invention is to provide a method ofnon-destructively and precisely diagnosing or measuring the location ofa conductor embedded in a non-conductive material. A specific example isa method of diagnosing or measuring the location of a water pipe or agas pipe buried under the ground.

[0021] A tenth object of the present invention is to provide a method ofnon-destructively and precisely diagnosing or measuring a structureincluding a conductor and a non-conductive material covering theconductor as to whether the conductor has a fracture. A specific exampleis a method of determining whether a bridge, an electric pole, or arailroad tie, which are made of prestressed concrete, has a fractureand/or measuring the location of such a fracture.

DISCLOSURE OF THE INVENTION

[0022] To achieve the above objects, the present invention provides anacoustic diagnosis/measurement apparatus using a pulse ofelectromagnetic force, as described in claim 1, comprising a coilattached to a surface of a structure including a conductor and anon-conductive material covering the conductor; a power supply unit forsupplying a current pulse to the coil; an acoustic transducer attachedto the surface of the structure or to a part of the conductor, the partbeing exposed from the non-conductive material; and a measurement unitfor measuring an output waveform of the acoustic transducer, wherebycorrosion of the conductor, adhesion strength of the conductor, thecover depth of the conductor, and/or the diameter of the conductor arediagnosed or measured.

[0023] In this apparatus, when the structure subjected to themeasurement is, for example, reinforced concrete, an acoustic wave isgenerated from an acoustic wave source at the location of thereinforcing iron rod directly excited by the magnetic field pulse andthe acoustic wave propagates through the structure to the surfacethereof. The acoustic wave propagating to the surface of the structurevaries depending on the degree of corrosion and/or adhesion of thereinforcing iron rod. Therefore, by analyzing the acoustic waveform, itis possible to diagnose or measure the degree of corrosion and theadhesion strength. The amplitude of the acoustic waveform also variesdepending on the diameter of the reinforcing iron rod and the coverdepth of the reinforcing iron rod. If the depth of the reinforcing ironrod is known, the diameter of the reinforcing iron rod can bedetermined. Conversely, if the diameter of the reinforcing iron rod isknown, the cover depth can be determined.

[0024] In this technique, because the reinforcing iron rod is directlyexcited by the magnetic field pulse, a very large acoustic waveform canbe obtained compared with that obtained in the conventional technique inwhich an ultrasonic wave generated by an ultrasonic source is reflectedfrom the reinforcing iron rod. Furthermore, in this technique accordingto the present invention, unlike the conventional percussion method, thedegree of corrosion, the strength of adhesion, the cover depth, and/orthe diameter of the reinforcing iron rod can be diagnosed or measurednon-destructively in a highly reliable fashion.

[0025] The present invention also provides an acousticdiagnosis/measurement apparatus using a pulse of electromagnetic force,as described in claim 2, comprising a coil attached to a surface of astructure including a conductor and a non-conductive material coveringthe conductor; a power supply unit for supplying a current pulse to thecoil; a plurality of acoustic transducers attached at differentlocations on the surface of the structure; and a measurement unit formeasuring acoustic propagation delays from outputs of the acoustictransducers, whereby the location of the conductor is measured.

[0026] In this apparatus, an acoustic wave is generated from an acousticwave source at the location of the reinforcing iron rod directly excitedby the magnetic field pulse and the acoustic wave propagates through thestructure to the surface thereof. On the basis of propagation delaytimes of the acoustic wave measured at different locations, the locationof the reinforcing iron rod can be precisely determinednon-destructively.

[0027] The present invention provides an acoustic diagnosis/measurementapparatus using a pulse of electromagnetic force, as described in claim3, comprising a coil attached to a surface of a structure including aconductor and a non-conductive material covering the conductor; a powersupply unit for supplying a current pulse to the coil; and adisplacement detector for optically measuring displacement of thesurface of the structure thereby measuring a vibration of the surface ofthe structure; whereby the location of the conductor, corrosion of theconductor, and/or adhesion strength of the conductor are diagnosed ormeasured.

[0028] In this apparatus, an acoustic wave is generated from an acousticwave source at the location of the reinforcing iron rod directly excitedby the magnetic field pulse and the acoustic wave propagates through thestructure to the surface thereof. By employing a laser interferometer asthe displacement detector, it is possible to detect the distribution ofsmall vibrations over the entire surface and it is also possible todetect the propagation mode of vibrations, and thus it is possible toobtain further detailed information in a non-destructive fashion.

[0029] Preferably, the acoustic transducer in claim 1, 2, or 3 is anelement for converting an acoustic signal into an electric signal,selected from a group consisting of an acoustic emission sensor, anacceleration sensor, and a microphone.

[0030] The displacement detector described in claim 3 may be a laserinterferometer for illuminating a surface of the structure with acoherent laser beam and detecting a phase difference as an interferencepattern of a reflected laser beam, the phase difference varyingdepending on a vibration of a surface of the structure.

[0031] The coil described in one of claims 1 to 3 may be a single coilor may include a plurality of subcoils. In the case in which a pluralityof subcoils are used, the plurality of subcoils are disposed coaxiallysuch that adjacent coils are in close contact with each other. The powersupply unit in claim 1, 2, or 3 may include charge storage capacitorsconnected in series to the respective subcoils and a power sourceconnected, via a common switch and in parallel, to each seriesconnection of one subcoil and one capacitor, whereby a current pulse isapplied to subcoils by turning on the common switch thereby generating amagnetic field pulse.

[0032] When the coil is formed using a plurality of subcoils, theinductance of each of subcoils forming the coil is smaller than is inthe case in which the coils is formed of a single coil, and thecapacitor of each charge storage capacitor can be reduced. This makes itpossible to reduce the time constant of a current pulse which flowsthrough each subcoil in response to turning on the common switch. Themagnetic field pulses generated by the subcoils are superimposed, andthus it is possible to generate an overall magnetic field pulse having alarge crest value and a small pulse width. The capability of generatinga magnetic field pulse with a large crest value and a small pulse widthmakes it possible to strongly excite a reinforcing iron rod, whichallows diagnosis/measurement to be performed non-destructively in a highreliable fashion.

[0033] It is desirable to add a magnet for generating a static magneticfield to the coil.

[0034] This makes it possible to further strongly excite the reinforcingiron rod and thus it makes possible to perform diagnosis/measurement ofa reinforcing iron rod located at deeper depth with respect to thesurface of the structure.

[0035] The measurement unit for measuring the output waveform in claim 1may measure the output waveform in the time domain, display the measuredoutput waveform, extract a feature associated with corrosion and/oradhesion from the waveform in the time domain, and display the extractedfeature, or may calculate a waveform in the frequency domain, that is, afrequency spectrum, by performing a Fourier transform on the originaloutput waveform, display the calculated waveform in the frequencydomain, extract a feature associated with corrosion and/or adhesion fromthe waveform in the frequency domain, and display information associatedwith the corrosion and/or adhesion.

[0036] This measurement unit is capable of instantly performingdiagnosis/measurement of corrosion and/or corrosion from the waveform inthe time domain or frequency domain.

[0037] The feature extracted from the waveform in the time domain may bea pattern, a shape factor, or a crest factor of the waveform in the timedomain, and the displaying of information associated with the corrosionand/or adhesion may include comparing the form factor or the crestfactor with a predetermined threshold value and displaying whether ornot there is a problem in terms of the corrosion and/or the adhesion.

[0038] The shape factor and the crest factor vary sensitively dependingon corrosion and/or adhesion, and thus it is possible to easily detectcorrosion and/or adhesion from the shape factor and the crest factor.The measured shape factor or crest factor is compared with apredetermined threshold value, and information whether there is aproblem in terms of corrosion/adhesion is displayed. Thus, any user cancorrectly perform diagnosis/measurement without having to have a highskill.

[0039] The feature extracted from the waveform in the time domain may bea similarity factor extracted from the shape of the envelope curve ofthe waveform in the time domain, and the displaying of informationassociated with the corrosion and/or adhesion may include comparing thesimilarity factor with a predetermined threshold value and displayingwhether or not there is a problem in terms of the corrosion and/or theadhesion.

[0040] Aging effects are reflected in the similarity factor, and thushigh-reliability diagnosis/measurement can be performed on the base ofthe similarity factor. The measured similarity factor is compared with apredetermined threshold value, and information whether there is aproblem in terms of corrosion/adhesion is displayed. Thus, any user cancorrectly perform diagnosis/measurement without having to have a highskill.

[0041] The feature extracted from the waveform in the time domain may bea normalized waveform obtained by dividing each value of the waveform inthe time domain by the effective value of the waveform in the timedomain or a waveform obtained by exponentiating the normalized waveform.

[0042] If the waveform in the time domain is normalized by dividing eachvalue of the waveform in the time domain by the effective value of thewaveform in the time domain, the feature of the original waveformbecomes clearer. The feature of the original waveform becomes furtherclearer by exponentiation. Thus, it becomes possible to performhigh-sensitive diagnosis/measurement.

[0043] The similarity factor may be extracted from the envelope curve ofthe normalized waveform and compared with a predetermined thresholdvalue. Depending on the comparison result, information indicatingwhether or not there is a problem in terms of the corrosion and/or theadhesion may be displayed.

[0044] Because the similarity factor is determined from the normalizedwaveform, it becomes possible for any user to easily perform correctdiagnosis/measurement in a further sensitive fashion.

[0045] The feature extracted from the waveform in the frequency domainmay be a waveform pattern in the frequency domain, and the displaying ofinformation associated with the corrosion and/or adhesion may includecomparing the waveform pattern with a predetermined pattern, anddisplaying whether or not there is a problem in terms of the corrosionand/or the adhesion.

[0046] In the vibration of a reinforcing iron rod excited by a pulse ofelectromagnetic force, the degree of freedom of vibration variesdepending on corrosion/adhesion of the reinforcing iron rod, and thusthe degree of corrosion/adhesion is very sensitively reflected in thefrequency spectrum. Because information is displayed which indicateswhether or not there is a problem in terms of corrosion/adhesiondetermined based on the comparison of the frequency spectrum with apredetermined reference frequency pattern, any user can easily performcorrect diagnosis/measurement without having to have a high skill.

[0047] The feature extracted from the waveform in the frequency domainmay be a normalized waveform obtained by dividing each value of thewaveform in the frequency domain by the effective value of the waveformin the frequency domain or a waveform obtained by exponentiating thenormalized waveform, and the displaying of information associated withthe corrosion and/or adhesion may include extracting the similarityfactor from the envelope curve of the normalized waveform, comparing thesimilarity factor with a predetermined threshold value, and displayingwhether or not there is a problem in terms of the corrosion and/or theadhesion.

[0048] The waveform in the frequency domain is very sensitive to thedegree of corrosion and/or adhesion strength. If this waveform in thefrequency domain is normalized by dividing each value of the waveform inthe frequency domain by the effective value, the feature of the originalwaveform is emphasized in the resultant normalized waveform. Thus,highly sensitive diagnosis/measure of corrosion/adhesion is possible.Furthermore, if the similarity factor is determined from the normalizedwaveform, high-sensitive and high-reliability diagnosis/measurement ispossible. The measured similarity factor is compared with apredetermined threshold value, and information whether there is aproblem in terms of corrosion/adhesion is displayed. Thus, any user cancorrectly perform diagnosis/measurement without having to have a highskill.

[0049] The displacement detector in claim 3 may be a laserinterferometer for illuminating a surface of the structure with acoherent laser beam and detecting a phase difference as an interferencepattern of a reflected laser beam, the phase difference varyingdepending on a vibration of a surface of the structure.

[0050] The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, asdescribed in claim 15, comprising the steps of attaching a coil to asurface of a structure including a conductor and a non-conductivematerial covering the conductor; applying a current pulse to the coilthereby generating a magnetic field pulse; inducing an eddy current inthe conductor by the magnetic field pulse; oscillating the conductor byinteraction between the eddy current and the magnetic field pulsethereby generating an acoustic wave; converting an acoustic signal ofthe acoustic wave into an electric signal by using an acoustictransducer attached to the surface of the structure or attached to apart of the conductor, the part of the conductor being exposed from thenon-conductive material; and measuring the waveform of the electricsignal to perform diagnosis and/or measurement in terms of corrosionand/or adhesion of the conductor.

[0051] In this method, when the structure subjected to the measurementis, for example, reinforced concrete, an acoustic wave is generated froman acoustic wave source at the location of the reinforcing iron roddirectly excited by the magnetic field pulse and the acoustic wavepropagates through the structure to the surface thereof. The acousticwave propagating to the surface of the structure varies depending on thedegree of corrosion and/or adhesion of the reinforcing iron rod.Therefore, by analyzing the acoustic waveform, it is possible todiagnosing or measuring the degree of corrosion and the adhesionstrength.

[0052] In this technique, because the reinforcing iron rod is directlyoscillated by the magnetic field pulse, a very large acoustic waveformcan be obtained compared with that obtained in the conventionaltechnique in which an ultrasonic wave generated by an ultrasonic sourceis reflected from the reinforcing iron rod. Thus, the degree ofcorrosion, the strength of adhesion, the cover depth, and/or thediameter of the reinforcing iron rod can be diagnosed or measurednon-destructively.

[0053] The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, asdescribed in claim 16, comprising the steps of attaching a coil to asurface of a structure including a conductor and a non-conductivematerial covering the conductor; applying a current pulse to the coilthereby generating a magnetic field pulse; inducing an eddy current inthe conductor by the magnetic field pulse; oscillating the conductor byinteraction between the eddy current and the magnetic field pulsethereby generating an acoustic wave; converting an acoustic signal ofthe acoustic wave into electric signals by using a plurality of acoustictransducers attached at different locations on the surface of thestructure; and measuring propagation delay times of the acoustic wavecorresponding to the respective electric signals; and measuring thelocation of the conductor on the basis of the propagation delay times.

[0054] In this method, an acoustic wave is generated from an acousticwave source at the location of the reinforcing iron rod directly excitedby the magnetic field pulse and the acoustic wave propagates through thestructure to the surface thereof. On the basis of propagation delaytimes of the acoustic wave measured at different locations, the locationof the reinforcing iron rod can be precisely determinednon-destructively.

[0055] The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, asdescribed in claim 17, comprising the steps of attaching a coil to asurface of a structure including a conductor and a non-conductivematerial covering the conductor; applying a current pulse to the coilthereby generating a magnetic field pulse; inducing an eddy current inthe conductor by the magnetic field pulse; oscillating the conductor byinteraction between the eddy current and the magnetic field pulsethereby generating an acoustic wave; detecting an optical displacementcorresponding to a surface vibration of the structure generated by theacoustic wave thereby diagnosing the location of the conductor and thestate of the structure.

[0056] In this method, an acoustic wave is generated from an acousticwave source at the location of the reinforcing iron rod directly excitedby the magnetic field pulse and the acoustic wave propagates through thestructure to the surface thereof. By employing a laser interferometer asthe displacement detector, it is possible to detect the distribution ofsmall vibrations over the entire surface and it is also possible todetect the propagation mode of vibrations, and thus it is possible toperform further detailed diagnosis in a non-destructive fashion.

[0057] The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, asdescribed in claim 18, comprising the steps of disposing a coil on asurface of a non-conductive material covering a conductor; applying acurrent pulse to the coil thereby generating a magnetic field pulse;inducing an eddy current in the conductor by the magnetic field pulse;oscillating the conductor by interaction between the eddy current andthe magnetic field pulse thereby generating an acoustic wave; convertingan acoustic signal of the acoustic wave into an electric signal by usingan acoustic transducer attached to the surface of the structure; andmeasuring the waveform of the electric signal to measure the diameter ofthe conductor or measure the cover depth of the conductor.

[0058] In this method, the amplitude of the acoustic waveform variesdepending on the diameter of the reinforcing iron rod and the coverdepth of the reinforcing iron rod. If the depth of the reinforcing ironrod is known, the diameter of the reinforcing iron rod can bedetermined. Conversely, if the diameter of the reinforcing iron rod isknown, the cover depth can be determined.

[0059] The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, asdescribed in claim 19, comprising the steps of disposing a coil at alocation exactly above a connecting part of a plurality of conductorsbound with each other via a binding member; applying a current pulse tothe coil thereby generating a magnetic field pulse; inducing an eddycurrent in a conductor facing the coil by the magnetic field pulse;oscillating the conductor by interaction between the eddy current andthe magnetic field pulse thereby generating an acoustic wave; convertingan acoustic signal of the acoustic wave into an electric signal by usingan acoustic transducer attached to the conductor facing the coil and byusing an acoustic transducer attached to another conductor bound withthe former conductor; and comparing the waveform of the electric signaloutput by the acoustic transducer attached to the conductor facing thecoil with the waveform of the electric signal output by the acoustictransducer attached to the other conductor, thereby performing diagnosisand/or measurement as to whether the binding member is in a securelyfastened state.

[0060] In this method, the magnitude of a vibration propagating into theconductor from the other conductor facing the coil varies depending onthe fastening degree. Thus, the fastening degree can be diagnosed ormeasured. This method is useful in particular when a set of a bolt and anut is used as the binding member.

[0061] The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, asdescribed in claim 21, comprising the steps of disposing a coil on asurface of a non-conductive material covering a conductor; applying acurrent pulse to the coil thereby generating a magnetic field pulse;inducing an eddy current in the conductor by the magnetic field pulse;oscillating the conductor by interaction between the eddy current andthe magnetic field pulse thereby generating an acoustic wave; convertingan acoustic signal of the acoustic wave into an electric signal by usingan acoustic transducer attached to a part of the conductor, the part ofthe conductor being exposed from the non-conductive material; changingthe location of the coil disposed on the surface of the non-conductivematerial; and measuring a change in the electric signal caused by thechange in the location of the coil there by measuring the location ofthe conductor.

[0062] In this method, the conductor is oscillated most strongly whenthe coil comes to a location closest to the conductor. Thus, thelocation of the conductor can be diagnosed or measured. This method isuseful in particular when the conductor is an underground water pipe orgas pipe.

[0063] The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, asdescribed in claim 23, comprising the steps of attaching a coil to asurface of a structure including a conductor and a non-conductivematerial covering the conductor; applying a current pulse to the coilthereby generating a magnetic field pulse; inducing an eddy current inthe conductor by the magnetic field pulse; oscillating the conductor byinteraction between the eddy current and the magnetic field pulsethereby generating an acoustic wave; converting an acoustic signal ofthe acoustic wave into an electric signal by using an acoustictransducer attached to a part of the conductor, the part of theconductor being exposed from the non-conductive material; and diagnosingwhether the conductor has a fracture, on the basis of the strength ofthe electric signal and, if necessary, diagnosing the location of thefracture of the conductor by changing the location of the coil disposedon the surface of the structure and measuring a change in the electricsignal caused by the change in the location of the coil.

[0064] In this method, an acoustic signal propagating through areinforcing iron rod is attenuated by a fracture, and thus it ispossible to detect whether or not there is a fracture. Furthermore, if achange in attenuation is measured while changing the location of thecoil disposed on the surface of a structure, it is possible to detectthe location of the fracture. This method is useful in particular whenthe structure is made of prestressed concrete, such as a bridge, anelectric pole, or a railroad tie made of prestressed concrete.

[0065] Thus, according to the present invention, it is possible tonon-destructively and precisely diagnose/measure not only the locationof an reinforcing iron rod in concrete but also corrosion, adhesionstrength, and/or rust of the reinforcing iron rod and further aseparation or a crack of concrete in diagnosis/measurement of astructure made of reinforced concrete, such as a tunnel, a bridge, abuilding, a retaining wall, a dam, or a civil construction. This makesit possible to prevent a structure made of reinforced concrete frombreaking down or prevent a piece of concrete from separating from themain part. Thus it becomes possible to precisely predict the remaininglife of a structure made of reinforced concrete and performmaintenance/management of the structure made of reinforced concrete in ahighly reliable fashion.

[0066] The cover depth and/or the diameter of a reinforcing iron rod canalso be measured.

[0067] It is also possible to easily determine whether a binding membersuch as a set of a bolt and a nut is securely fastened.

[0068] It is also possible to easily determine the location of a waterpipe or a gas pipe buried in the ground.

[0069] It is also possible to diagnose whether a reinforcing iron rodhas a fracture.

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the accompanying drawings. Note that the embodimentsdescribed with reference to the accompanying drawing are presented forthe purpose of illustration and ease of understanding of the inventionand are not intended to limit the invention.

[0071] FIGS. 1(a) and 1(b) are conceptual diagrams showing theembodiment of the acoustic diagnosis/measurement apparatus using a pulseof electromagnetic force according to claim 1 of the present inventionand the method therefor, FIG. 1(a) shows a manner in which an acoustictransducer is attached to a surface of concrete, FIG. 1(b) shows amanner in which the acoustic transducer is attached to an exposed partof an iron rod.

[0072] FIGS. 2(a) and 2(b) are diagrams showing the shape of a testsample of reinforced concrete used herein in the first example and alsoshowing a measurement system, wherein FIG. 2(a) is a plan view and FIG.2(b) is a side view thereof.

[0073] FIGS. 3(a) and 3(b) are diagrams showing measured acousticwaveforms, wherein an acoustic waveform observed for the normal block isshown in FIG. 3(a) and an acoustic waveform observed for the crackedblock is shown in FIG. 3(b).

[0074]FIG. 4 is a schematic diagram showing an acousticdiagnosis/measurement apparatus using a pulse of electromagnetic forceaccording to claim 2 of the present invention.

[0075]FIG. 5(a) to 5(c) show the surface shape of reinforced concreteused in an embodiment and a method of producing the reinforced concrete,wherein FIG. 5(a) shows the surface shape of the reinforced concrete,FIG. 5(b) shows an outer frame used to produce the reinforced concrete,and FIG. 5(c) shows the external appearance of produced reinforcedconcrete.

[0076]FIG. 6 is a diagram showing propagation delay times in thereinforced concrete, measured at different distances from the acousticwave source.

[0077]FIG. 7 is a graph showing a manner in which the velocity of anacoustic wave propagating through concrete is determined frompropagation delay times measured at various distances from an acousticwave source.

[0078]FIG. 8(a) shows a coil and a power supply unit according to aconventional technique, and FIG. 8(b) shows a coil and a power supplyunit according to the present invention.

[0079] FIGS. 9(a) and 9(b) show an example of the waveform of a currentpulse applied to a coil from a power source and an example of a measuredacoustic signal generated thereby, wherein the example shown in FIG.9(a) is according to a conventional technique, and the example shown inFIG. 9(b) is according to the present invention.

[0080] FIGS. 10(a), 10(b), and 10(c) are diagrams showing waveforms inthe time domain output by the acoustic transducers attached to therespective test blocks (A), (B), and (C) and measured by the measurementunit.

[0081] FIGS. 11(a), 11(b), and 11(c) are diagrams showing waveforms inthe time domain output by the acoustic transducers directly attached toreinforcing iron rods of the respective test blocks (A), (B), and (C)and measured by the measurement unit.

[0082]FIG. 12 is a table showing the shape factors SF and the crestfactors CF for the respective test blocks (A), (B), and (C).

[0083]FIG. 13(a) shows the envelope curves determined for the respectivetest blocks (A), (B), and (C), and FIG. 13(b) shows the correspondinglogarithmic inverse envelope curves.

[0084] FIGS. 14(a), 14(b), and 14(c) respectively show the time-domainwaveform, the normalized waveform, and the square of the normalizedwaveform, obtained for the test block (A).

[0085] FIGS. 15(a) and 14(b) respectively show the cube and the quarticof the normalized waveform of the test block (A).

[0086] FIGS. 16(a), 16(b), and 16(c) respectively show the time-domainwaveform, the normalized waveform, and the square of the normalizedwaveform, obtained for the test block (B).

[0087] FIGS. 17(a) and 17(b) respectively show the cube and the quarticof the normalized waveform of the test block (B).

[0088] FIGS. 18(a), 18(b), and 18(c) respectively show the time-domainwaveform, the normalized waveform, and the square of the normalizedwaveform, obtained for the test block (C).

[0089] FIGS. 19(a) and 19(b) respectively show the cube and the quarticof the normalized waveform of the test block (C).

[0090] FIGS. 20(a), 20(b), and 20(c) respectively show frequency-domainwaveforms of the test blocks (A), (B), and (C), determined from thetime-domain waveforms determined in the third example for the testblocks (A), (B), and (C).

[0091] FIGS. 21(a), 21(b), and 21(c) respectively show frequency-domainwaveforms of the test blocks (A), (B), and (C), determined from thetime-domain waveforms determined in the fourth example for the testblocks (A), (B), and (C).

[0092]FIG. 22(a) is a diagram showing a method of measuring the diameteror the cover depth of a reinforcing iron rod according to the presentinvention, and FIG. 22(b) is a graph showing a measurement result.

[0093] FIGS. 23(a) and 23(b) are diagrams showing a method of diagnosingor measuring the secureness of a binding member, according to thepresent invention, wherein FIG. 23(a) is a side view of a conductor 21and a conductor 22 bound together via a bolt 22 and a nut 23, and FIG.23(b) is a plan view thereof.

[0094] FIGS. 24(a) to 24(d) are diagrams showing a measurement resultobtained when the bolt and the nut are securely fastened, wherein FIGS.24(a) and 24(b) show output waveforms of an acoustic transducer 14Rattached to the conductor 21 located closer to a coil, and FIGS. 24(c)and 24(d) show output waveforms of an acoustic transducer 14L attachedto the conductor 22 bound with the conductor 21 by the bolt and the nut.

[0095] FIGS. 25(a) to 25(d) are diagrams showing a measurement resultobtained when the bolt and the nut are in a loosely coupled state,wherein FIGS. 25(a) and 25(b) show output waveforms of the acoustictransducer 14R attached to the conductor 21 located closer to a coil,and FIGS. 25(c) and 25(d) show output waveforms of the acoustictransducer 14L attached to the conductor 22 bound with the conductor 21by the bolt and the nut.

[0096] FIGS. 26(a) and 26(b) are diagrams showing a method of measuringthe location of a conductor embedded in a non-conductive material,wherein FIG. 26(a) is a side view showing a manner in which an acoustictransducer 14 is attached to an exposed part 33 of a water pipe 32buried in the ground 31 which is non-conductive, and a coil 12 isdisposed on the surface 34 of ground 31, and FIG. 26(b) is a plan viewthereof.

[0097] FIGS. 27(a) to 27(c) are graphs showing results of measurement ofthe location of a water pipe buried in the ground, wherein FIG. 27(a)shows the waveform of an acoustic signal detected by the coil disposedexactly above the water pipe, FIG. 27(b) shows a waveform detected bythe coil disposed on the ground at a location 60 mm apart from thelocation exactly above the water pipe, FIG. 27(c) shows a waveformdetected by the coil disposed on the ground at a location 180 mm apartfrom the location exactly above the water pipe.

[0098]FIG. 28 is a diagram showing a method of diagnosing whether aconductor embedded in a non-conductive material has a fracture and amethod of measuring the location of the fracture.

BEST MODE FOR CARRYING OUT THE INVENTION

[0099] Embodiments of the present invention are described in detailbelow with reference to drawings.

[0100] First, an embodiment of an acoustic diagnosis/measurementapparatus using a pulse of electromagnetic force according to claim 1 ofthe present invention and a method therefor are described.

[0101] Herein, by way of example, the structure including a conductorand a non-conductive material covering the conductor subjected todiagnosis/measurement is assumed to be a structure made of concretereinforced with iron rods.

[0102] The apparatus of the present embodiment is capable of makingdiagnosis/measurement in terms of corrosion, adhesion, cover depth, anddiameters of iron rods.

[0103] FIGS. 1(a) and 1(b) are conceptual diagrams showing theembodiment of the acoustic diagnosis/measurement apparatus using a pulseof electromagnetic force according to claim 1 of the present inventionand the method therefor, wherein FIG. 1(a) shows a manner in which anacoustic transducer is attached to a surface of concrete, and FIG. 1(b)shows a manner in which the acoustic transducer is attached to anexposed part of an iron rod.

[0104] In FIG. 1(a), the acoustic diagnosis/measurement apparatus usinga pulse of electromagnetic force 10 includes a coil of an electric wire12 attached to a surface of a reinforced concrete block 11 which is astructure to be examined, a power supply unit 13 for applying a currentpulse to the coil 12, an acoustic transducer 14 attached to the surfaceof the reinforced concrete block 11, and a measurement unit 15 connectedto the acoustic transducer 14 via a signal cable 17.

[0105] The coil 12 includes four coils each formed of 7 turns of aconductive wire with a diameter of, for example, 1.6 mm wound around arectangular-shaped frame with a size of 50 mm×30 mm wherein those fourcoils are disposed coaxially and closely. The coil 12 is attached to thesurface of the reinforced concrete block 11 to be examined. The powersupply unit 13 is designed to apply a current pulse to the coil 12 via apower cable 16. The power supply unit 13 may be constructed in variousmanners depending on the size of the reinforced concrete block 11 andthe location of the reinforcing iron rod 11 a so that a desirabledriving pulse is applied.

[0106] As for the acoustic transducer 14, a known acoustic transducermay be employed to detect a weak vibration and convert the detectedvibration into an electric signal. The resultant electric signal issupplied to the measurement unit 15 via the signal cable 17.

[0107] As for the measurement unit 15, for example, a commerciallyavailable apparatus known as acoustic analyzer may be employed. Thesignal detected by the acoustic transducer 14 is amplified by anamplifier, and unnecessary components of the signal are removed by usinga filter or the like. Acoustic analysis is then performed on the basisof the resultant signal. Another apparatus may also be used as themeasurement unit 15. For example, in a case in which it is needed tomeasure only the waveform of the signal detected by the acoustictransducer 14, an oscilloscope or similar equipment may be employed.

[0108] In the acoustic diagnosis apparatus using a pulse ofelectromagnetic force 10 constructed in the above-described manneraccording to the present invention, if a current pulse is applied to thecoil 12, a magnetic field pulse is generated toward the inside of thereinforced concrete 11, and the magnetic field pulse induces an eddycurrent in the reinforcing iron rod 11 a which is conductive. A magneticfield is generated by the eddy current and it interacts with themagnetic field of the magnetic field pulse. As a result, the reinforcingiron rod 11 a is oscillated. Herein, if the conductor 11 a is made of amagnetic material, reinforcing iron rod 11 a is further oscillated by aforce associated with magnetic energy.

[0109] If the reinforcing iron rod 11 a is oscillated, an acoustic waveis generated from the reinforcing iron rod 11 a. The generated acousticwave propagates to the surface and is detected by the acoustictransducer 14. The detected acoustic signal is converted into anelectrical signal by the acoustic transducer 14 and supplied to themeasurement unit 15 via the signal cable 17. The measurement unit 15analyzes the waveform of the received electric signal to determine thedegree of corrosion of the reinforcing iron rod 11 a or determinewhether the concrete 11 b has a crack. If the reinforcing iron rod 11 ahas corroded, the acoustic wave generated by the reinforcing iron rod 11a is absorbed by a corroded portion, and attenuation of the acousticwave occurs, which results in a reduction in the amplitude of thewaveform observed by the measurement unit 15. Also in a case in whichadhesion between the reinforcing iron rod and the concrete is weak, theamplitude of the waveform detected by the measurement unit 15 becomessmall. A crack in the concrete results in attenuation of the acousticwave, and thus the amplitude of the waveform detected by the measurementunit 15 becomes small. As described above, by comparing the amplitude ofthe acoustic wave, it is possible to detect the degree of damage of thereinforced concrete 11.

[0110] As shown in FIG. 1(b), it is also possible to detect corrosion oradhesion of a reinforcing iron rod by attaching the acoustic transducer14 to an exposed portion of the reinforcing iron rod and directlydetecting a vibration of the reinforcing iron rod.

[0111] Now, a first example is described.

[0112] In this first example, an example of measurement using theacoustic diagnosis/measurement apparatus using a pulse ofelectromagnetic force according to claim 1 of the present invention isdescribed.

[0113] FIGS. 2(a) and 2(b) are diagrams showing the shape of a testsample of reinforced concrete used herein in the first example and alsoshowing a measurement system, wherein FIG. 2(a) is a plan view and FIG.2(b) is a side view thereof.

[0114] As shown in FIGS. 2(a) and 2(b), the test sample of reinforcedconcrete 11 includes rectangular-shaped concrete 11 b with a size of 200mm×150 mm×100 mm and a reinforcing iron rod 11 a with a diameter of 13mm embedded at a cover depth d of 30 mm measured from the upper surfaceof the concrete 11 b and at a distance of 57 mm from the lower surface.The coil 12 is disposed on the surface of the reinforced concrete 11 ata location exactly above the reinforcing iron rod 11 a. The acoustictransducers 14 a and 14 b are disposed on the surface of the reinforcedconcrete 11, at symmetrical locations opposing each other via thereinforcing iron rod 11 a.

[0115] In the present example, a test sample of reinforced concrete withno crack in concrete 11 b (normal test block) and a test sample ofreinforced concrete with a crack extending in concrete 11 b and reachinga reinforcing iron rod 11 a (test block with crack) were prepared andthey were excited under the same conditions. Acoustic waves weredetected by the acoustic transducers 14 a and 14 b and the waveformswere compared.

[0116] The coil 12 used herein was formed by winding 25 turns anelectric wire with a diameter of 1.0 mm around a core with a size of 30mm×70 mm and had an internal resistance of 0.2 Ω. A current pulse with acrest value of 1000 Å and a width of 1.5 ms was applied to the coil 12thereby exciting the reinforcing iron rod 11 a.

[0117] FIGS. 3(a) and 3(b) are diagrams showing measured acousticwaveforms, wherein an acoustic waveform observed for the normal block isshown in FIG. 3(a) and an acoustic waveform observed for the crackedblock is shown in FIG. 3(b).

[0118] In FIGS. 3(a) and 3(b), CH1 and CH2 denote output waveforms ofthe acoustic transducers 14 a and 14 b, respectively, and CH3 denotesthe waveform of the current pulse. The horizontal axis represents a timein units of 0.5 ms/div and the vertical axis represents the strength ofthe waveforms CH1 and CH2, wherein zero points of CH1 and CH2 areshifted from each other.

[0119] As can be seen from FIGS. 3(a) and 3(b), the crack significantlyattenuates the acoustic wave generated by the reinforcing iron rod 11 aexcited by the current pulse.

[0120] Thus, it is possible to determine whether concrete has a crack.

[0121] Now, an embodiment of an acoustic diagnosis/measurement apparatususing a pulse of electromagnetic force according to claim 2 of thepresent invention and a corresponding method of acousticdiagnosis/measurement using a pulse of electromagnetic force aredescribed below.

[0122] This apparatus is capable of measuring the location of areinforcing iron rod in reinforced concrete.

[0123]FIG. 4 is a conceptual diagram showing an acousticdiagnosis/measurement apparatus using a pulse of electromagnetic forceaccording to claim 2 of the present invention and a correspondingmethod.

[0124] As shown in FIG. 4, an acoustic location detector 20 includes acoil of an electric wire 12 attached to a surface of a reinforcedconcrete block 11, a power supply unit 13 (similar to that shown in FIG.1, although not shown in FIG. 4) for applying a current pulse to thecoil 12, a plurality of acoustic transducers 14 (14 a, 14 b, and 14 c)attached to the surface of the reinforced concrete block 11, and ameasurement unit 15 (similar to that shown in FIG. 1 although not shownin FIG. 4) connected to the acoustic transducers 14 via a signal cable17 (similar to that shown in FIG. 1 although not shown in FIG. 4).

[0125] The plurality of acoustic transducers 14 are disposed around thecoil 12, and the coil 12 is excited by applying a current pulse theretothereby generating an acoustic wave from the reinforcing iron rod 11 a.The acoustic wave is detected and converted into electric signals by therespective acoustic transducers 14, and the resultant electric signalsare supplied to the measurement unit 15. The measurement unit 15determines propagation delay times, that is, times needed for theacoustic wave to propagate from the acoustic wave source to therespective acoustic transducers 14.

[0126] The propagation velocity of the acoustic wave in the concrete 11b can be regarded to be substantially constant. Therefore, from thepropagation velocity v and the delay times t, it is possible todetermine, the distances r from the acoustic wave source to therespective acoustic transducer 14, that is, the distances from thereinforcing iron rod 11 a to the respective acoustic transducer 14. Fromthose distances, it is possible to determine the location of theacoustic wave source, that is, the location of the reinforcing iron rod11 a.

[0127] For example, in a case in which the reinforcing iron rod 11 a hasthe shape of a rod such as that shown in FIG. 4, if the distances ra,rb, and rc (=v·ta, v·tb, and v·tc) from the acoustic wave source to thereinforcing iron rod 11 a are determined from the propagation delaytimes ta, tb, and tc detected by the acoustic transducers 14 a, 14 b and14 c, and if spheres with radii ra, rb, and rc, respectively, are drawnso that the center of each sphere is located at the correspondinglocation of the acoustic transducer 14, then the location of thereinforcing iron rod l a is given by a common point of contact ofspheres.

[0128] Although in the above-described example, a plurality of acoustictransducers 14 are disposed on the surface of the concrete 11 and thepropagation delay times at the locations of the acoustic transducers 14are simultaneously measured for a single acoustic signal, thepropagation delay times at various locations may be measured using asingle acoustic transducer 14 in such a manner that the location of theacoustic transducer 14 is changed across the surface of the concrete 11,an acoustic signal is generated at each location and the propagationdelay time is measured.

[0129] Now, a second example is described.

[0130] In this second example, an example of measurement using theacoustic diagnosis/measurement apparatus using a pulse ofelectromagnetic force according to claim 2 of the present invention isdescribed.

[0131]FIG. 5(a) to 5(c) show the surface shape of reinforced concreteused in an embodiment and a method of producing the reinforced concrete,wherein FIG. 5(a) shows the shape of a surface of the reinforcedconcrete, FIG. 5(b) shows an outer frame used to form the reinforcedconcrete, and FIG. 5(c) shows the external appearance of producedreinforced concrete. As shown in FIG. 5(b), the reinforced concrete usedin this example was produced by pouring concrete into the outer frame,in the center of which a reinforcing iron rod 11 a covered, except forits center, with an elastic plastic sheet was disposed, so that only thecentral portion of the reinforcing iron rod 11 a was brought intocontact with the concrete 11 b and the other portion was not in contactwith the concrete 11 b. In this structure, a generated acoustic wavepropagates into the concrete from the center of the reinforcing iron rod11 a, and thus the acoustic wave source can be regarded as a pointsource.

[0132] As shown in FIG. 5(a), the center of the reinforced concrete 11was taken as the origin and the horizontal and vertical axes were takenas x and y axes, respectively. The coil was disposed at the origin, andthe location of the acoustic transducer was represented by coordinates(x, y). The propagation delay time of the acoustic wave detected by theacoustic transducer was measured for various values of coordinates (x,y). The exciting coil, the acoustic transducer, and the current pulseused herein are similar to those used in the first example.

[0133]FIG. 6 is a diagram showing propagation delay times in thereinforced concrete, measured at different distances from the acousticwave source.

[0134] In FIG. 6, CH1 and CH2 denote acoustic waveforms detected by theacoustic transducer placed at coordinates (−1, 0) and (3, 2),respectively, shown in FIG. 5(a), and CH3 denotes the waveform of thecurrent pulse. The horizontal axis represents the time in units of 0.1ms/div and the vertical axis represent the voltage corresponding to thestrength of the acoustic waveforms denoted by CH1 and CH2, wherein thezero point of the voltage axis for CH1 was shifted from that for CH2.

[0135] As can be seen from FIG. 6, the acoustic waveform CH1 detected ata position near the acoustic wave source appears at substantially thesame time as the current pulse rises. In contrast, the acoustic waveformCH2 detected at a position distant from the acoustic wave source appearsafter a rather large delay from the leading edge of the current pulse.

[0136] Thus, it is possible to detect the distance from the acousticpower source by detecting the propagation delay time.

[0137]FIG. 7 is a graph showing a manner in which the velocity of anacoustic wave propagating through concrete is determined frompropagation delay times measured at various distances from an acousticwave source.

[0138] In FIG. 7, the distance from the acoustic wave source denotes thedistance between each coordinate point shown in FIG. 6(a) and theacoustic wave source. The propagation delay time was measured in thesame manner as described above with reference to FIG. 7.

[0139] As can be seen from FIG. 7, the velocity of the acoustic wavepropagating through concrete can be regarded as constant.

[0140] Therefore, the distance to the acoustic wave source can bedetermined from the propagation delay time described with reference withFIG. 6 and the velocity of the acoustic wave described with referencewith FIG. 7. If the distance to the acoustic wave source is measured ata large number of points, the location of the reinforcing iron rod canbe given by a location which satisfies all measured distances.

[0141] As described above, the acoustic location detector using a pulseof electromagnetic force according to the present invention is capableof non-destructively detecting the location of a reinforcing iron rod.

[0142] Now, an acoustic diagnosis/measurement apparatus according toclaim 3 of the present invention is described.

[0143] This acoustic diagnosis/measurement apparatus is similar to theacoustic diagnosis/measurement apparatus 10 except that the acoustictransducer 14 is replaced by a surface displacement detector and asurface vibration of a structure 11 to be examined is detected insteadof an acoustic wave.

[0144] Although any type of detector may be employed as the surfacedisplacement detector as long as it is capable of measuring a smalldisplacement, it is desirable to use a laser interferometer becauseprecise and detailed diagnosis is possible by illuminating the entiresurface of the structure 11 to be diagnosed with coherent laser lightand detecting an interference pattern indicating the phase difference ofa reflected light caused by the surface vibration of the structure 11.

[0145] The coil and the power supply unit used in the acousticdiagnosis/measurement apparatus according to the present invention aredescribed below.

[0146]FIG. 8(a) shows a coil and a power supply unit according to aconventional technique, and FIG. 8(b) shows a coil and a power supplyunit according to the present invention.

[0147] In the conventional technique, as shown in FIG. 2(a), the coil isconstructed in the form of a single piece of coil, and a current pulseis applied to the coil 12 in such a manner that the capacitor C ischarged by an AC voltage V supplied from commercial electric power andthe charge stored in the capacitor C is transferred to the coil 12 byturning on the switch SW which may be a mechanical switch or asemiconductor switch.

[0148] On the other hand, in the present invention, as shown in FIG.2(b), the coils is divided into a plurality of subcoils 12 each havingsmall inductance, and the subcoils 12 are disposed coaxially and closelysuch that magnetic fields generated by the respective coils aresuperimposed. A capacitor C is connected in series to each subcoil, andfour series circuits each consisting of one coil 12 and one capacitor Care connected in parallel to a common power supply V via a common switchSW which may be a mechanical switch or a semiconductor switch.

[0149] In this circuit configuration, the coil in each series circuithas small inductance and the capacitor in each series circuit has smallcapacitance, and thus a current pulse with a small time constant can besupplied when the switch SW is turned on. The magnetic field pulsesgenerated by the respective coils are superimposed and thus a resultantoverall magnetic pulse has a small pulse width and a large crest value.

[0150] FIGS. 9(a) and 9(b) show an example of the waveform of a currentpulse applied to a coil from a power source and an example of a measuredacoustic signal generated thereby, wherein the example shown in FIG.9(a) is according to a conventional technique, and the example shown inFIG. 9(b) is according to the present invention. The acoustic wavesignal was measured using the acoustic diagnosis/measurement apparatususing a pulse of electromagnetic force according to the presentinvention. Reinforced concrete including a reinforcing iron rod 13D(deformed reinforcing iron rod with a diameter of 13 mm) with a coverdepth d of 30 mm was used as a test sample. As can be seen from FIG. 9,the coil and the power supply constructed in the above-described manneraccording to the present invention are capable of supplying a currentpulse with a much smaller pulse width and a much larger height than canbe achieved by the conventional technique.

[0151] Furthermore, by employing the coil and the power supply accordingto the present invention, a waveform detected by the acoustic emission(AE) sensor, that is, the output waveform of the acoustic transducerbecomes much greater than can be achieved by the conventional technique.

[0152] As described above, by forming the coil and the power supply inthe above-described manner according to the present invention, itbecomes possible to generate a magnetic field pulse with a small pulsewidth and a large crest value, which can strongly excite a reinforcingiron rod.

[0153] A measurement unit used in the apparatus described in claims 1 to3 is described below.

[0154] The measurement unit according to the present invention samplesthe output waveform of the acoustic transducer, converts the sampledvalue into digital data, stores the resultant digital data into amemory, performs a particular calculation on the digital data via a CPUaccording to a particular signal processing program, and stores theresult into a memory or displays the result on a display. The particularsignal processing program includes a program of displaying a time-domainwaveform of the output waveform, a program of calculating afrequency-domain waveform, that is, frequency spectrum obtained byperforming a Fourier transform on the time-domain waveform of the outputwaveform, and other various signal processing programs which will bedescribed later. The sampling apparatus, the analog-to-digitalconverter, the memory, the CPU, and the display may be those which arecommercially available.

[0155] By employing the measurement unit constructed in the abovedescribed manner, it is possible to measure the waveform in the timedomain and display information associated with corrosion and/oradhesion. Furthermore, it is possible to extract a feature associatedwith corrosion and/or adhesion from the waveform in the time domain anddisplay the extracted feature. It is also possible to calculate thewaveform in the frequency domain, that is, the Fourier transformspectrum of the output waveform, extract a feature associated withcorrosion and/or adhesion from the waveform in the frequency domain, anddisplay information associated with corrosion and/or adhesion.

[0156] Now, a third example is described below.

[0157] In this third example, it is demonstrated that a featureassociated with corrosion and/or adhesion can be extracted from awaveform in the time domain.

[0158] Three different types of test blocks of reinforced concretelisted below were prepared and compared with each other.

[0159] (A) Normal reinforced concrete.

[0160] (B) Normal reinforced concrete was fatigued using a fatigue testmachine until a slight crack starting from a reinforcing iron rod wasproduced.

[0161] (C) Normal reinforced concrete was fatigued using a fatigue testmachine beyond the state of the test sample (B) until adhesion between areinforcing iron rod and concrete was lost.

[0162] The test blocks were all produced using 13D reinforcing iron rods(deformed reinforcing iron rods with a diameter of 13 mm) so as to haveexternal dimensions of 200 mm×150 mm× and 100 mm and a cover depth d of30 mm.

[0163] A coil 12 and an acoustic transducer 14 were attached to asurface of each test block, and a current pulse with a crest value of2000 Å and a pulse width of 350 μs was applied to each coil 12 therebyexciting the reinforcing iron rod.

[0164] FIGS. 10(a), 10(b), and 10(c) are diagrams showing waveforms inthe time domain output by the acoustic transducers attached to therespective test blocks (A), (B), and (C) and measured by the measurementunit.

[0165] As can be seen from those figures, for the normal reinforcedconcrete block (A), a waveform having a triangle-like shape having asymmetry axis and a vertex along the time axis was obtained.

[0166] On the other hand, for the test block (B) having a crack, awaveform having a rectangle-like shape having a symmetry axis and avertex along the time axis was obtained.

[0167] However, for the test block (C) having substantially no adhesionbetween the reinforcing iron rod and the concrete, substantially nooutput waveform was observed.

[0168] As described above, by displaying waveforms in the time domainmeasured by the measurement unit of the apparatus according to thepresent invention, it is possible to detect differences in corrosionand/or adhesion of reinforcing iron rods from the waveforms.

[0169] Now, a fourth example is described below.

[0170] In this fourth example, it is demonstrated that a featureassociated with corrosion and/or adhesion can be extracted fromwaveforms in the time domain also in a case in which an acoustictransducer (AE sensor) is attached to an exposed part of a reinforcingiron rod of reinforced concrete as shown in FIG. 1(b).

[0171] Test blocks similar to those used in the third example were used,and an experiment was performed in a similar manner to the example 3except for the attaching location of each acoustic transducer.

[0172] FIGS. 11(a), 11(b), and 11(c) are diagrams showing waveforms inthe time domain output by the acoustic transducers directly attached toreinforcing iron rods of the respective test blocks (A), (B), and (C)and measured by the measurement unit.

[0173] As can be seen from those figures, substantially no outputwaveform was observed for the normal reinforced concrete (A). This isbecause strong adhesion between the reinforcing iron rod and theconcrete causes a vibration produced by exciting the reinforcing ironrod to be quickly attenuated.

[0174] On the other hand, for the test block (B) having a crack, awaveform having a triangle-like shape having a symmetry axis and avertex along the time axis was obtained.

[0175] However, for the test block (C) having substantially no adhesionbetween the reinforcing iron rod and the concrete, a waveform having atriangle-like shape having a symmetry axis and a vertex along the timeaxis was obtained, but the waveform has a long tail extending along thetime axis. This is because adhesion between the reinforcing iron rod andthe concrete was lost and a space was created between the reinforcingiron rod and the concrete, and thus a vibration of the reinforcing ironrod attenuates gradually. As a result, the vibration continues for along time.

[0176] As described above, by displaying waveforms in the time domainmeasured by the measurement unit of the apparatus according to thepresent invention, it is possible to detect differences in corrosionand/or adhesion of reinforcing iron rods from the waveforms also in thecase in which the acoustic transducer is attached directly to areinforcing iron rod.

[0177] A process, performed by the measurement unit to extract a featureassociated with corrosion and/or adhesion from the shape factor or thecrest factor of the waveform in the time domain and display informationwhether or not there is a problem associated with corrosion and/oradhesion, is described below.

[0178] First, formulas used in the signal processing program performedby the measurement unit to determine the shape factor and the crestfactor are described.

[0179] Let x_(i) denote each data value of a waveform in the timedomain, and let N denote the total number of data.

[0180] An average value x_(av) is defined by the following formula:$x_{av} = \frac{\sum\limits_{i = 1}^{N}\quad x_{i}}{N}$

[0181] An effective value x_(rms) is defined by the following formula:$x_{r\quad m\quad s} = \sqrt{\frac{\sum\limits_{i = 1}^{N}\quad x_{i}^{2}}{N}}$

[0182] A peak value x_(p) is defined by the following formula:$x_{p} = {\max\limits_{i \in N}\left\{ x_{i} \right\}}$

x _(p) =ma _(iε) x _(N) {x _(i)}

[0183] The shape factor SF is defined by the following formula:${SF} = \frac{x_{r\quad m\quad s}}{\overset{\_}{x}}$

[0184] The crest factor CF is defined by the following formula:${CF} = \frac{x_{p}}{x_{r\quad m\quad s}}$

[0185] A fifth example is described below.

[0186] In this fifth example, the shape factor SF and the crest factorCF were determined in accordance with above-described formulas (1) to(5) from the waveforms in the time domain measured in the example 3 forthe respective test blocks (A), (B), and (C), and a comparison was made.

[0187]FIG. 12 is a table showing the shape factors SF and the crestfactors CF for the respective test blocks (A), (B), and (C).

[0188] As can be seen from FIG. 12, the shape factor SF and the crestfactor CF significantly vary depending on the test blocks, that is,depending on the adhesion of the reinforcing iron rod.

[0189] As described above, the measurement unit calculates the shapefactor SF and the crest factor CF of a structure to be examined inaccordance with the signal processing program and compares thecalculated shape factor SF and the crest factor CF with respect tothreshold values predetermined as, for example, 1.50 for the shapefactor and 5.50 for the crest factor in FIG. 12. It is determinedwhether there is no problem depending on whether the shape factor or thecrest factor of the structure under examination are greater than thecorresponding threshold value, and information indicating whether or notthere is a problem is displayed.

[0190] A process, performed by the measurement unit to determine asimilarity factor by extracting a feature associated with corrosionand/or adhesion from the shape of the envelope curve of the waveform inthe time domain and display information whether or not there is aproblem associated with corrosion and/or adhesion, is described below.

[0191] First, formulas used in the signal processing program performedby the measurement unit to determine the similarity factor aredescribed.

[0192] First, the absolute value x_(i) is determined for each data valueof the waveform in the time domain. The absolute values are put oneafter another in the same order as that in which the waveform wassampled, and an envelope curve which smoothly envelopes the series ofthe absolute values is calculated. Let y_(i) denote each data value ofthe envelope curve.

[0193] A probability P(y_(i)) is defined by the following formula:${P\left( y_{i} \right)} = \frac{y_{i}}{\sum\limits_{i = 1}^{N}\quad y_{i}}$

[0194] Let P_(a)(y_(i)) be the probability P(y_(i)) for the structure inan initial state, and P_(b)(y_(i)) be probability P(y_(i)) for thestructure used for a particular period of time, then the amount ofinformation IF(y_(i)) can be defined by the following formula:${{IF}\left( y_{i} \right)} = {\log \frac{P_{a}\left( y_{i} \right)}{P_{b}\left( y_{i} \right)}}$

[0195] The similarity factor SF is defined by the following formula:${SF} = {\sum\limits_{i = 1}^{N}{\log \frac{P_{a}\left( y_{i} \right)}{p_{b}\left( y_{i} \right)}}}$

[0196] Now, a sixth example is described below.

[0197] In this sixth example, the envelope curves were determined fromthe waveforms in the time domain, determined in the example 3 for therespective test blocks (A), (B), and (C), and a comparison in terms ofthe similarity factor was performed.

[0198]FIG. 13(a) shows the envelope curves determined for the respectivetest blocks (A), (B), and (C), and FIG. 13(b) shows the correspondinglogarithmic inverse envelope curves. Herein, the logarithmic inverseenvelope curve refers to an envelop curve for the logarithm value of theinverse of the probability P(y_(i)).

[0199] As can be seen from FIG. 13(a), the envelope curves of the testblocks (B) and (C) are significantly different from that of the testblock (A). Thus, by comparing an envelope curve such as that for thetest block (B) or (C) with respect to an envelope curve in an initialstate such as that for the test block (A), it is possible to detect anoccurrence of corrosion and/or a reduction in adhesion.

[0200] As can be seen from FIG. 13(b), also in the logarithmic inverseenvelope curves, a clear difference relative to the initial stateappears, and thus the similarity factor obtained by adding thedifferences along the time axis is used to diagnose corrosion and/oradhesion.

[0201] As described above, in accordance with the signal processingprogram, the measurement unit calculates the envelope curve, thelogarithmic inverse envelope curve, and the similarity factor andcompares the similarity factor with the predetermined threshold value.Depending on whether the similarity factor is greater than or equal toor smaller than the threshold value, information indicating whether ornot there is a problem is displayed.

[0202] The measurement unit may extract a feature associated withcorrosion and/or adhesion from a normalized waveform obtained bydividing each value of a waveform in the time domain by the effectivevalue of the waveform or from a waveform obtained by exponentiating thenormalized waveform whereby information associated with the corrosionand/or adhesion may be displayed. This technique is described in furtherdetail below.

[0203] The normalized waveform can be obtained by dividing the datavalue X_(i) of the waveform in the time domain by the effective valuex_(rms) given by formula (2).

[0204] With reference to a seventh example, the technique is describedfurther.

[0205] In this seventh example, the normalized waveform and theexponentiated waveform thereof are calculated for the respective testblocks (A), (B), and (C) from the time-domain waveforms measured in theexample 3 for the respective test blocks (A), (B), and (C).

[0206] FIGS. 14(a), 14(b), and 14(c) respectively show the time-domainwaveform, the normalized waveform, and the square of the normalizedwaveform, obtained for the test block (A).

[0207] FIGS. 15(a) and 14(b) respectively show the cube and the quarticof the normalized waveform of the test block (A).

[0208] FIGS. 16(a), 16(b), and 16(c) respectively show the time-domainwaveform, the normalized waveform, and the square of the normalizedwaveform, obtained for the test block (B).

[0209] FIGS. 17(a) and 17(b) respectively show the cube and the quarticof the normalized waveform of the test block (B).

[0210] FIGS. 18(a), 18(b), and 18(c) respectively show the time-domainwaveform, the normalized waveform, and the square of the normalizedwaveform, obtained for the test block (C).

[0211] FIGS. 19(a) and 19(b) respectively show the cube and the quarticof the normalized waveform of the test block (C).

[0212] As can be seen from FIGS. 14 to 19, the normalized waveform andthe exponentiated waveform thereof indicate more clearly the differencein the degree of corrosion and/or adhesion among the test blocks (A),(B), and (C) than can be indicated by the time-domain waveform. Inparticular, the waveforms obtained by means of high-order exponentiationsignificantly differ depending on the degree of corrosion and/oradhesion.

[0213] As described above, by evaluating the normalized waveform or theexponentiated waveform thereof, it is possible to perform high-sensitivedetection of corrosion and/or adhesion.

[0214] As described above, in accordance with the signal processingprogram, the measurement unit extracts a feature by calculating thenormalized waveform and the exponentiated waveform thereof from thetime-domain waveform, determines, on the basis of comparison withthreshold values, whether or not there is a problem associated withcorrosion and/or adhesion, and displays the result.

[0215] The measurement unit may extract a feature associated withcorrosion and/or adhesion from a frequency-domain waveform and maydisplay information indicating whether or not there is a problemassociated with corrosion and/or adhesion, as described in detail below.

[0216] The frequency-domain waveform is determined by the measurementunit by performing a Fourier transform on a time-domain waveform inaccordance with the signal processing program.

[0217] With reference to an eighth example, the technique is describedin further detail below.

[0218] In this eighth example, the frequency-domain waveform isdetermined by performing a Fourier transform on each of the time-domainwaveforms determined in the third or fourth example for the test blocks(A), (B), and (C), and the resultant frequency-domain waveforms of thetest blocks (A), (B), and (C) are compared with each other.

[0219] FIGS. 20(a), 20(b), and 20(c) respectively show frequency-domainwaveforms of the test blocks (A), (B), and (C), determined from thetime-domain waveforms determined in the third example for the testblocks (A), (B), and (C).

[0220] As can be seen from FIG. 20(a), in the case of the test block (A)of normal reinforced concrete, the frequency spectrum includescomponents distributed randomly and substantially continuously in afrequency range of 20 kHz to 80 kHz.

[0221] On the other hand, as can be seen from FIG. 20(b), in the case ofthe test block (B) of reinforced concrete having a crack, particularfrequency components appear at particular intervals.

[0222] In the case of the test block (C) in which adhesion of areinforcing iron rod was lost, as can be seen from FIG. 20(c),particular frequency components appear at particular intervals, althoughthe tendency is not strong compared with the text block (B). Anotherfeature of this test block (C) is that the frequency-domain waveformincludes a large component near 150 kHz.

[0223] The difference between FIGS. 20(a) and 20(b), that is, betweenthe text block (A) and the test block (B) is very great. This makes itpossible to easily detect the difference even in the case in which thedifference cannot be easily detected from the time-domain waveforms.

[0224] FIGS. 21(a), 21(b), and 21(c) respectively show frequency-domainwaveforms of the test blocks (A), (B), and (C), determined from thetime-domain waveforms determined in the fourth example for the testblocks (A), (B), and (C) by using the acoustic transducers attacheddirectly to reinforcing iron rods.

[0225] As can be seen from those figures, in the case in which theacoustic transducers are directly attached to reinforcing iron rods,particular frequency components appear at particular intervals withdecreasing adhesion, as in the case shown in FIG. 20.

[0226] As described above, in accordance with the signal processingprogram, the measurement unit calculates the frequency-domain waveformfrom a time-domain waveform and compares the resultant frequency-domainwaveform with a reference pattern thereby determining the similarity.The similarity is then compared with a threshold value of similarity.Depending on whether the similarity is equal to or smaller than thethreshold value, it is determined whether or not there is a problem, andinformation indicating the result is displayed.

[0227] The measurement unit may determine the normalized waveform or theexponentiated waveform of the normalized waveform from afrequency-domain waveform in a similar manner as described above withreference to the sixth or seventh example, and may perform ahigh-sensitive extraction of a feature associated with corrosion and/oradhesion using the normalized waveform or the exponentiated waveform ofthe normalized waveform. Furthermore, the similarity factor may becalculated from the normalized waveform or the exponentiated waveform ofthe normalized waveform, and the resultant similarity factor may becompared with a predetermined threshold value thereby performing ahigh-sensitive detection of whether the similarity factor of a structureunder examination is equal to or smaller than the threshold value. Inaccordance with the result, information indicating whether or not thereis a problem is displayed.

[0228] A method of measuring the cover depth of reinforced concrete orthe diameter of a reinforcing iron rod according to claim 18 of thepresent invention is described below.

[0229]FIG. 22(a) is a diagram showing a method of measuring the diameteror the cover depth of a reinforcing iron rod according to the presentinvention, and FIG. 22(b) is a graph showing a measurement result.

[0230] As described in FIG. 22(a), a coil 12 is attached to a surface ofreinforced concrete 11, at a location exactly above a reinforcing ironrod 11 a, and an acoustic transducer 14 is attached to the surface ofthe reinforced concrete 11. The reinforcing iron rod 11 a is thenexcited by a magnetic field pulse generated by the coil 12, therebygenerating an acoustic signal from the reinforcing iron rod 11 a. Theacoustic signal is converted into an electric signal by the acoustictransducer 14 and supplied to a measurement unit 15. The measurementunit 15 extracts a feature value such as the peak-to-peak value of thecrest value of the acoustic signal. If the cover depth d is known, thediameter of the reinforcing iron rod can be determined from theextracted feature value and the cover depth d on the basis of thepredetermined correspondence among the feature value, the diameter ofreinforcing iron rod, and the cover depth. In a case in which the coverdepth d is unknown, the cover depth d can be determined in accordancewith the technique disclosed in claim 2 of the present invention.

[0231] In a case in which the diameter of the reinforcing iron rod isknown but the cover depth d is unknown, the cover depth d is determinedfrom the detected feature value and the diameter of the reinforcing ironrod on the basis of the predetermined correspondence among the featurevalue, the diameter of the reinforcing iron rod, and the cover depth.

[0232] In FIG. 22(b), the vertical axis represents the feature value. Inthis specific example, the peak-to-peak value of the crest value isemployed as the feature value. The horizontal axis represents the coverdepth d. As shown in an insertion in FIG. 22(b), the dependence of thefeature value on the cover depth d was determined for various diametersof the reinforcing iron rods 10 d, 13 d, 16 d, 19 d, and 25 d (deformedreinforcing iron rods with diameters of 10 mm, 13 mm, 16 mm, 19 mm, and25 mm).

[0233] As can be seen from FIG. 22(b), the feature value depends on boththe diameter of the reinforcing iron rod and the cover depth d. Thus, onthe basis of the dependence determined above, it is possible todetermine the cover depth d or the diameter of the reinforcing iron rod.

[0234] A method of diagnosing/measuring whether a binding member issecurely fastened according to claim 19 of the present invention isdescribed below.

[0235] FIGS. 23(a) and 23(b) are diagrams showing a method of diagnosingor measuring the secureness of a binding member, according to thepresent invention, wherein FIG. 23(a) is a side view of a conductor 21and a conductor 22 bound together via a bolt 23 and a nut 24, and FIG.23(b) is a plan view thereof.

[0236] A coil 12 is disposed exactly above the bolt 22 binding theconductor 21, and acoustic transducers 14R and 14L are attached to thesurfaces of the respective conductors 21 and 22. If a magnetic filedpulse is generated by the coil 12, an eddy current is induced in thesurface of the conductor 21 and a magnetic field generated by the eddycurrent interacts with the magnetic field of the magnetic field pulsewhereby the conductor 21 is oscillated. If the bolt 23 and the nut 24are screwed in a securely fastened state, an acoustic signal generatedin the conductor 21 propagates to the conductor 22 without having asignificant attenuation and thus acoustic signals detected by theacoustic transducer 14R and the acoustic transducer 14L become nearlyequal in magnitude. However, if the bolt 23 and the nut 24 are screwedin a loose state, an acoustic signal generated in the conductor 21 doesnot propagate easily into the conductor 22, and thus a difference occursbetween acoustic signals detected by the acoustic transducer 14R and theacoustic transducer 14L.

[0237] Thus, it is possible to evaluate whether binding members are in asecurely fastened state.

[0238] A ninth example is described below.

[0239] In this ninth example 9, it is demonstrated that the fasteningstate of binding members can be evaluated using the method ofdiagnosing/measuring a fastening state of a binding member according tothe present invention.

[0240] Two aluminum plates (200×300×3t) were bound with six sets ofstainless steel bolts ad nuts (M10×15). A current pulse with a crestvalue of 2000 Å and a pulse width of 350 μs was applied to the coil.

[0241] FIGS. 24(a) to 24(d) shows a measurement result obtained when thebolts and nuts were in a securely fastened state, wherein FIGS. 24(a)and 24(b) show output waveforms of the acoustic transducer 14R attachedto the conductor 21 facing the coil, and FIGS. 24(c) and 24(d) showoutput waveforms of the acoustic transducer 14L attached to theconductor 22 bound with the conductor 21 using the bolts and nuts.

[0242] Note that FIGS. 24(a) and 24(c) show waveforms obtained bypassing the original output waveforms of the acoustic transducer througha bandpass (BP) filter (having a passband of 20 kHz to 500 kHz) therebyremoving frequency components lower than 20 kHz, while FIGS. 24(b) and24(d) show waveforms including whole frequency components up to 500 kHz.

[0243] As can be seen from those figures, when the bolt and the nut aresecurely fastened, the output waveform of the acoustic transducer 14L issubstantially equal to that of the acoustic transducer 14R.

[0244] FIGS. 25(a) to 25(d) are diagrams showing a measurement resultobtained when the bolt and the nut are in a loosely coupled state,wherein FIGS. 25(a) and 25(b) show output waveforms of the acoustictransducer 14R attached to the conductor 21 located closer to a coil,and FIGS. 25(c) and 25(d) show output waveforms of the acoustictransducer 14L attached to the conductor 22 bound with the conductor 21by the bolt and the nut. Note that FIGS. 25(a) and 25(c) show waveformsobtained by passing the original output waveforms of the acoustictransducer through a bandpass (BP) filter (having a passband of 20 kHzto 500 kHz) thereby removing frequency components lower than 20 kHz,while FIGS. 25(b) and 25(d) show waveforms including whole frequencycomponents up to 500 kHz.

[0245] As can be seen from those figures, when the bolt and the nut arenot securely fastened, the output waveform of the acoustic transducer14L is smaller in amplitude than that of the acoustic transducer 14R.

[0246] As described above, this method of the present invention makes itpossible to diagnose or measure whether a binding member is securelyfastened.

[0247] This method can also be used to detect a crack in a honeycombstructure used in a bridge or the like. Furthermore, the method can alsobe used to determine whether connection is well welded.

[0248] A method of measuring the location of a conductor embedded in anon-conductive material according to claim 21 of the present inventionis described below.

[0249] FIGS. 26(a) and 26(b) are diagrams showing a method of measuringthe location of a conductor embedded in a non-conductive material,wherein FIG. 26(a) is a side view showing a manner in which an acoustictransducer 14 is attached to an exposed part 33 of a water pipe 32buried in the ground 31 which is non-conductive, and a coil 12 isdisposed on the surface 34 of ground 31, and FIG. 26(b) is a plan viewthereof.

[0250] If a magnetic field pulse is generated by the coil 12, an eddycurrent is induced in the surface of the water pipe 32, and the waterpipe 32 is oscillated as a result of interaction between the magneticfield associated with the eddy current and the magnetic field of themagnetic field pulse. An acoustic wave generated by the oscillation ofthe water pipe 32 propagates to the exposed part 33 of the water pipe 32and is detected by the acoustic transducer 14. The strength of theacoustic signal becomes highest when the coil 12 is put at a locationexactly above the water pipe 32. By changing the location of the coil 12and looking for a location at which the strength of the acoustic signalbecomes highest, the location of the water pipe 32 can be detected.

[0251] Now, a tenth example is described.

[0252] In this tenth example, it is demonstrated that the location of aconductor embedded in a non-conductive material can be detected by theabove-described method according to the present invention.

[0253] FIGS. 27(a) to 27(c) are graphs showing results of measurement ofthe location of a water pipe buried in the ground, wherein FIG. 27(a)shows the waveform of an acoustic signal detected by the coil disposedexactly above the water pipe, FIG. 27(b) shows a waveform detected bythe coil located 60 mm apart from the location exactly above the waterpipe, FIG. 27(c) shows a waveform detected by the coil located 180 mmapart from the location exactly above the water pipe.

[0254] As can be seen from those figures, the strength of the acousticsignal becomes highest when the coil is located exactly above the waterpipe, the strength of the acoustic signal decreases with the distancebetween the coil and the position exactly above the water pipe. Thus, ifthe location of the coil is changed and the location at which theacoustic signal becomes highest is determined, the location of the waterpipe must be exactly below the location at which the acoustic signalbecomes highest.

[0255] A method of determining whether a conductor embedded in anon-conductive material has a fracture and/or determining the locationof such a fracture according to claim 23 of the present invention isdescribed below.

[0256]FIG. 28 is a diagram showing a method of diagnosing whether aconductor embedded in a non-conductive material has a fracture and amethod of measuring the location of the fracture.

[0257] An acoustic transducer 14 is attached to an exposed part 43 of areinforcing iron rod 42 embedded in reinforced concrete 41 with anelongated shape. A coil 12 is attached to a surface of the elongatedreinforced concrete 41. An eddy current is induced in the surface of areinforcing iron rod by generating a magnetic field pulse from the coil12. As a result, the reinforcing iron rod 42 is excited by theinteraction between the magnetic field associated with the eddy currentand the magnetic field of the magnetic field pulse. An acoustic wave isgenerated by the excited reinforcing iron rod 42 and propagates throughthe reinforcing iron rod 42. The acoustic wave propagating through thereinforcing iron rod 42 is detected by the acoustic transducer 14attached to the exposed part 43 of the reinforcing iron rod 42. If thereinforcing iron rod 42 has a fracture at some location 44, the strengthof the detected acoustic signal is small, and thus the reinforcing ironrod 42 can be regarded as having a fracture. By changing the location ofthe coil 12 across the surface of the elongated reinforced concrete 41and detecting a position at which the acoustic signal abruptly becomesstrong, the location 44 of the fracture can be determined.

[0258] As described above, the present invention makes it possible todetermine whether a reinforcing iron rod has a fracture and furtherdetermine the location of such a fracture.

[0259] Although the present invention has been described above withreference to specific embodiments, the invention is not limited to thoseembodiments but various modifications, additions, and eliminations arepossible without departing from the spirit and the scope of theinvention. It should be understood that the scope is defined by theclaims appended hereto.

[0260] Industrial Applicability

[0261] According to the present invention, as described above, aconductor in a structure including the conductor and a non-conductivematerial covering the conductor can be directly and strongly excited bya pulse of electromagnetic force. Thus, for example, when a reinforcingiron rod in reinforced concrete is excited, a very large acousticsignal, which is influenced by corrosion and/or adhesion of thereinforcing iron rod, is obtained. This makes it possible tonon-destructively and precisely diagnose/measure the location,corrosion, adhesion strength, and/or rust of the reinforcing iron rodand further a separation or a crack of the concrete, regardless of thethickness of the concrete and regardless of the degree of degradation.

[0262] Therefore, it becomes possible to diagnose/measure, very easilyin a highly reliable fashion, a structure made of reinforced concretesuch as a tunnel, a bridge, a building, retaining wall, dam, and civilengineering construction, thereby making it possible to performmaintenance/management of the structure made of reinforced concrete in ahighly reliable fashion.

[0263] Furthermore, according to the method of acousticdiagnosis/measurement using a pulse of electromagnetic force of thepresent invention, it is possible to measure the cover depth of areinforcing iron rod and/or the diameter of reinforcing iron rod.Furthermore it is also possible to determine whether a binding membersuch as a set of a bolt and a nut is securely fastened. The location ofa water pipe or a gas pipe buried in the ground can also be detected. Itis also possible to determine whether a reinforcing iron rod has afracture. Such diagnosis/measurement can be performed easily and in ahighly reliable fashion.

1. An acoustic diagnosis/measurement apparatus using a pulse ofelectromagnetic force, comprising a coil attached to a surface of astructure including a conductor and a non-conductive material coveringthe conductor; a power supply unit for supplying a current pulse to thecoil; an acoustic transducer attached to the surface of the structure orto a part of the conductor, the part being exposed from thenon-conductive material; and a measurement unit for measuring an outputwaveform of the acoustic transducer, whereby corrosion of the conductor,adhesion strength of the conductor, the cover depth of the conductor,and/or the diameter of the conductor are diagnosed or measured.
 2. Anacoutic diagnosis/measurement apparatus using a pulse of electromagneticforce, comprising a coil attached to a surface of a structure includinga conductor and a non-conductive material covering the conductor; apower supply unit for supplying a current pulse to the coil; a pluralityof acoustic transducers attached at different locations on the surfaceof the structure; and a measurement unit for measuring acousticpropagation delays from outputs of the acoustic transducers, whereby thelocation of the conductor is measured.
 3. An acouticdiagnosis/measurement apparatus using a pulse of electromagnetic force,comprising: a coil attached to a surface of a structure including aconductor and a non-conductive material covering the conductor; a powersupply unit for supplying a current pulse to the coil; and adisplacement detector for optically measuring displacement of thesurface of the structure thereby measuring a vibration of the surface ofthe structure, whereby the location of the conductor, corrosion of theconductor, and/or adhesion strength of the conductor are diagnosed ormeasured.
 4. An acoutic diagnosis/measurement apparatus using a pulse ofelectromagnetic force, according to one of claims 1 to 3, wherein theacoustic diagnosis/measurement apparatus using a pulse ofelectromagnetic force includes a plurality of subcoils, the plurality ofsubcoils being disposed coaxially such that adjacent subcoils are inclose contact with each other; and the power supply unit includes chargestorage capacitors connected in series to the respective coils and apower source connected, via a common switch and in parallel, to eachseries connection of one coil and one capacitor whereby a current pulseis applied to coils by turning on the switch thereby generating amagnetic field pulse.
 5. An acoustic diagnosis/measurement apparatususing a pulse of electromagnetic force, according to one of claims 1 to3, wherein a magnet for generating a static magnetic field is added tothe coil.
 6. An acoustic diagnosis/measurement apparatus using a pulseof electromagnetic force, according to one of claims 1 to 3, wherein theacoustic transducer is an element for converting an acoustic signal intoan electric signal, selected from a group consisting of an acousticemission sensor, an acceleration sensor, and a microphone.
 7. An acouticdiagnosis/measurement apparatus using a pulse of electromagnetic forceaccording to claim 1, wherein the measurement unit for measuring theoutput waveform measures the output waveform in the time domain,displays the measured output waveform, extracts a feature associatedwith corrosion and/or adhesion from the waveform in the time domain, anddisplays the extracted feature, or the measurement unit for measuringthe output waveform calculates a waveform in the frequency domain, thatis, a frequency spectrum, by performing a Fourier transform on theoriginal output waveform, displays the calculated waveform in thefrequency domain, extracts a feature associated with corrosion and/oradhesion from the waveform in the frequency domain, and displaysinformation associated with the corrosion and/or adhesion.
 8. An acouticdiagnosis/measurement apparatus using a pulse of electromagnetic forceaccording to claim 7, wherein the feature extracted from the waveform inthe time domain is a pattern, a shape factor, or a crest factor of thewaveform in the time domain; and the displaying of informationassociated with the corrosion and/or adhesion includes comparing theform factor or the crest factor with a predetermined threshold value anddisplaying whether or not there is a problem in terms of the corrosionand/or the adhesion.
 9. An acoutic diagnosis/measurement apparatus usinga pulse of electromagnetic force according to claim 7, wherein thefeature extracted from the waveform in the time domain is a similarityfactor extracted from the shape of the envelope curve of the waveform inthe time domain; and the displaying of information associated with thecorrosion and/or adhesion includes comparing the similarity factor witha predetermined threshold value and displaying whether or not there is aproblem in terms of the corrosion and/or the adhesion.
 10. An acouticdiagnosis/measurement apparatus using a pulse of electromagnetic forceaccording to claim 7, wherein the feature extracted from the waveform inthe time domain is a normalized waveform obtained by dividing each valueof the waveform in the time domain by the effective value of thewaveform in the time domain or a waveform obtained by exponentiating thenormalized waveform.
 11. An acoustic diagnosis/measurement apparatususing a pulse of electromagnetic force according to claim 10, wherein asimilarity factor is extracted from the envelope curve of the normalizedwaveform and compared with a predetermined threshold value, andinformation indicating whether or not there is a problem in terms of thecorrosion and/or the adhesion is displayed.
 12. An acouticdiagnosis/measurement apparatus using a pulse of electromagnetic forceaccording to claim 7, wherein the feature extracted from the waveform inthe frequency domain is a waveform pattern in the frequency domain; andthe displaying of information associated with the corrosion and/oradhesion includes comparing the waveform pattern with a predeterminedpattern, and displaying whether or not there is a problem in terms ofthe corrosion and/or the adhesion.
 13. An acoutic diagnosis/measurementapparatus using a pulse of electromagnetic force according to claim 7,wherein the feature extracted from the waveform in the frequency domainis a normalized waveform obtained by dividing each value of the waveformin the frequency domain by the effective value of the waveform in thefrequency domain or a waveform obtained by exponentiating the normalizedwaveform; and the displaying of information associated with thecorrosion and/or adhesion includes extracting the similarity factor fromthe envelope curve of the normalized waveform, comparing the similarityfactor with a predetermined threshold value, and displaying whether ornot there is a problem in terms of the corrosion and/or the adhesion.14. An acoutic diagnosis/measurement apparatus using a pulse ofelectromagnetic force according to claim 3, wherein the displacementdetector is a laser interferometer for illuminating a surface of thestructure with a coherent laser beam and detecting a phase difference asan interference pattern of a reflected laser beam, the phase differencevarying depending on a vibration of a surface of the structure.
 15. Amethod of acoustic diagnosis/measurement using a pulse ofelectromagnetic force, comprising the steps of: attaching a coil to asurface of a structure including a conductor and a non-conductivematerial covering the conductor; applying a current pulse to the coilthereby generating a magnetic field pulse; inducing an eddy current inthe conductor by the magnetic field pulse; oscillating the conductor byinteraction between the eddy current and the magnetic field pulsethereby generating an acoustic wave; converting an acoustic signal ofthe acoustic wave into an electric signal by using an acoustictransducer attached to the surface of the structure or attached to apart of the conductor, the part of the conductor being exposed from thenon-conductive material; and measuring the waveform of the electricsignal to perform diagnosis and/or measurement in terms of corrosionand/or adhesion of the conductor.
 16. A method of acousticdiagnosis/measurement using a pulse of electromagnetic force, comprisingthe steps of: attaching a coil to a surface of a structure including aconductor and a non-conductive material covering the conductor; applyinga current pulse to the coil thereby generating a magnetic field pulse;inducing an eddy current in the conductor by the magnetic field pulse;oscillating the conductor by interaction between the eddy current andthe magnetic field pulse thereby generating an acoustic wave; convertingan acoustic signal of the acoustic wave into electric signals by using aplurality of acoustic transducers attached at different locations on thesurface of the structure; and measuring propagation delay times of theacoustic wave corresponding to the respective electric signals; andmeasuring the location of the conductor on the basis of the propagationdelay times.
 17. A method of acoustic diagnosis/measurement using apulse of electromagnetic force, comprising the steps of: attaching acoil to a surface of a structure including a conductor and anon-conductive material covering the conductor; applying a current pulseto the coil thereby generating a magnetic field pulse; inducing an eddycurrent in the conductor by the magnetic field pulse; oscillating theconductor by interaction between the eddy current and the magnetic fieldpulse thereby generating an acoustic wave; detecting an opticaldisplacement corresponding to a surface vibration of the structuregenerated by the acoustic wave thereby diagnosing the location of theconductor and the state of the structure.
 18. A method of acousticdiagnosis/measurement using a pulse of electromagnetic force, comprisingthe steps of: attaching a coil to a surface of a structure including aconductor and a non-conductive material covering the conductor; applyinga current pulse to the coil thereby generating a magnetic field pulse;inducing an eddy current in the conductor by the magnetic field pulse;oscillating the conductor by interaction between the eddy current andthe magnetic field pulse thereby generating an acoustic wave; convertingan acoustic signal of the acoustic wave into an electric signal by usingan acoustic transducer attached to the surface of the structure; andmeasuring the waveform of the electric signal to measure the diameter ofthe conductor or measure the cover depth of the conductor.
 19. A methodof acoustic diagnosis/measurement using a pulse of electromagneticforce, comprising the steps of: disposing a coil at a location exactlyabove a connecting part of a plurality of conductors bound with eachother via a binding member; applying a current pulse to the coil therebygenerating a magnetic field pulse; inducing an eddy current in aconductor facing the coil by the magnetic field pulse; oscillating theconductor by interaction between the eddy current and the magnetic fieldpulse thereby generating an acoustic wave; converting an acoustic signalof the acoustic wave into an electric signal by using an acoustictransducer attached to the conductor facing the coil and by using anacoustic transducer attached to another conductor bound with the formerconductor; and comparing the waveform of the electric signal output bythe acoustic transducer attached to the conductor facing the coil withthe waveform of the electric signal output by the acoustic transducerattached to the other conductor, thereby performing diagnosis and/ormeasurement as to whether the binding member is in a securely fastenedstate.
 20. A method of acoustic diagnosis/measurement using a pulse ofelectromagnetic force, according to claim 19, wherein the binding memberis a set of a bolt and a nut.
 21. A method of acousticdiagnosis/measurement using a pulse of electromagnetic force, comprisingthe steps of: disposing a coil on a surface of a non-conductive materialcovering a conductor; applying a current pulse to the coil therebygenerating a magnetic field pulse; inducing an eddy current in theconductor by the magnetic field pulse; oscillating the conductor byinteraction between the eddy current and the magnetic field pulsethereby generating an acoustic wave; converting an acoustic signal ofthe acoustic wave into an electric signal by using an acoustictransducer attached to a part of the conductor, the part of theconductor being exposed from the non-conductive material; changing thelocation of the coil disposed on the surface of the non-conductivematerial; and measuring a change in the electric signal caused by thechange in the location of the coil there by measuring the location ofthe conductor.
 22. A method of acoustic diagnosis/measurement using apulse of electromagnetic force according to claim 21, wherein theconductor is a water pipe or a gas pipe buried in the ground; and thenon-conductive material is the ground.
 23. A method of acousticdiagnosis/measurement using a pulse of electromagnetic force, comprisingthe steps of: disposing a coil on a surface of a structure including aconductor and a non-conductive material covering the conductor; applyinga current pulse to the coil thereby generating a magnetic field pulse;inducing an eddy current in the conductor by the magnetic field pulse;oscillating the conductor by interaction between the eddy current andthe magnetic field pulse thereby generating an acoustic wave; convertingan acoustic signal of the acoustic wave into an electric signal by usingan acoustic transducer attached to a part of the conductor, the part ofthe conductor being exposed from the non-conductive material; anddiagnosing whether the conductor has a fracture, on the basis of thestrength of the electric signal and, if necessary, diagnosing thelocation of the fracture of the conductor by changing the location ofthe coil disposed on the surface of the structure and measuring a changein the electric signal caused by the change in the location of the coil.24. A method of acoustic diagnosis/measurement using a pulse ofelectromagnetic force according to claim 23, wherein the structure isprestressed concrete.